The electrical resistivity ρ and the thermopower α of the transition-metal pentatelluride system ${\mathrm{Hf}}_{1-X}{\mathrm{Zr}}_X{\mathrm{Te}}_{5-Y}{\mathrm{Sb}}_Y$ have been measured over a broad range of temperature, $10\mathrm{K}<T<\mathrm{}300\mathrm{}\mathrm{K}.$ The systematic Sb doping of these materials has been performed over a range from $0<Y<\mathrm{}0.75,$ where Y is the nominal Sb concentration. Both parent materials $({\mathrm{HfTe}}_5$ and ${\mathrm{ZrTe}}_5)$ exhibit an anomalous resistive peak, $T_P\approx 80\mathrm{K}$ for ${\mathrm{HfTe}}_5$ and $T_P\approx 145\mathrm{K}$ for ${\mathrm{ZrTe}}_5.$ Each parent material displays a large positive (p-type) thermopower $(\alpha >~+125\mathrm{}\mu \mathrm{V}/\mathrm{K})$ around room temperature, which undergoes a change to a large negative (n-type) thermopower $(\alpha <~-125\mu \mathrm{V}/\mathrm{K})$ below the peak temperature. At a specific level of Sb doping the resistive anomaly is no longer evident and results in a semimetallic temperature dependence. In addition the thermopower monotonically decreases with temperature with no change in sign as in the parent materials. X-ray-diffraction data reveals that the pentatelluride structure is still preserved at all doping concentrations.

• Received 30 January 2001

DOI:https://doi.org/10.1103/PhysRevB.64.121104